The lens celebrates its 10th anniversary this year!

Let us know how you get on if you follow this up.

Everyone knows that Pentax Users are malicious people. They fail to use a Canikon like everyone else and Bullguard are worried you'll buy another one!

Regarding the missing lens info in the exif, Pentax's don't write it to the exif metadata but to the maker notes instead and software has to be used to transfer it. However not all software being used is aware of recent lenses as it pre-dates them. The lens model in the maker notes exists purely as a number.
To transfer the missing lens info into the exif use an up-to-date tool such as Phil Harvey's exiftool link
Also see https://sourceforge.net/projects/exiftool/
If you had a windows PC I'd recommend using exiftoolgui (see this thread here) to transfer it immediately before any other processing is performed.
Fortunately a Mac variant exists named pyExifToolGUI at https://hvdwolf.github.io/pyExifToolGUI/ so that maybe worth investigating to perform a similar function (its based on the same code.)
If you haven't noticed, most gallery photos are missing the lens model unless its an oldish lens that's been used or a recent software version has been used to process the image. Exiftool fixes that missing info, though as you'll read in the linked to thread about it here, not everyone sees the point of it. Can't win 'em all!

Why aren't you upgrading to v1.30 which is the latest and enables PLM lenses?
I didn't notice any settings change when I updated.

Bristol Cameras definitely do Pentax, but they aren't in Leeds?? :

I looked in Hull Jessops recently and they had no Pentax gear despite a section labelled in lights 'Pentax'! I'm not sure I ever really understood Jessops after they spread out from their Leicester warehouse, even less since their Peter Jones takeover. It seems Jessops is now a no no for Pentax despite showing up as stockists on Ricoh's 'find a dealer' page.

To be honest, I'd have thought that aperture and f-stop meant the same thing. To quote from the English University Press Teach Yourself Photography book, "Aperture number, more commonly known as 'f' numbers, show the relationship between the diameter of the hole in the lens and the focal length of the lens."
Given that is a mathematical relationship it implies they are one and the same. Perhaps John can investigate why the difference noted in the PU exif extraction with the site developers. Having said that, other exif viewers also show differences so the site may be using data extracted by someone else's exif program.
FWIW the EUP book goes on to show a table of English F numbers and Continental F numbers which differ slightly Eg. English f/8 = Continental f/9. But given the book dates from 1940 I don't think that's anything to do with Brexit!
I can understand the thinking that an aperture could be defined as a physical measurement of the hole in the lens, as one might also say a window aperture is its measured size. Whereas an f stop is understandably the relationship between the diameter of the hole in the lens and the focal length of the lens which is fixed.
As David suggests, maybe variable aperture zoom lenses need an extra variable in the equation for the camera to ascertain a correct f number to use which wouldn't have been required in the days before zoom lenses and AE cameras.

Are these exceptions perhaps the ones that show OK? I find that when I've saved raw files to TIFF in Elements the final files loose the exif altogether, but save to jpg and they're fine.
PU's exif extractor does seem to be a law unto itself and could do with a bit of investigating by the site developers.

As to David's query, the matter is explained (for better or worse) on DPR here.

The PU site exif extraction can be buggy so it could be just that.
This is the exif of one from your gallery (The ICM coloured pencils):
[Quote]Camera Maker: RICOH IMAGING COMPANY, LTD.
Camera Model: PENTAX K-S2
Lens: smc PENTAX-DA 50mm F1.8
Image Date: 2017-04-24 14:55:46 (no TZ)
Focal Length: 50.0mm (35mm equivalent: 75mm)
Aperture: ƒ/22.0
Exposure Time: 1.600 s
ISO equiv: 100
Exposure Bias: none
Metering Mode: Matrix
Exposure: shutter priority (semi-auto)
White Balance: Auto
Flash Fired: No (enforced)
Orientation: Normal
GPS Coordinate: undefined, undefined
Creator: R.SOUCIE
Copyright: R.SOUCIE
Software: Adobe Photoshop Lightroom 6.0 (Macintosh)
[/quote]The site exif has corrupted that one:
[quote="PU site exif"]Camera Make:

Camera Model: MPANY, LTD.
Date Taken: 2017-04-24 14:55:46
Exposure Program: Shutter priority
F-Stop: f/22
Aperture Value: f/8.9
Max Aperture Value: Undefined
ISO Speed Rating: 100
Focal Length: 50 mm
Lens: Undefined
Metering Mode: Pattern/Matrix
Exposure Time: 1.6 sec[/quote]Yet your orchids exif seems OK
[quote="PU site exif"]Camera Make: RICOH IMAGING COMPANY, LTD.
Camera Model: PENTAX K-S2
Date Taken: 2017-02-14 09:48:55
Exposure Program: Aperture priority
F-Stop: f/16
Aperture Value: f/8
Max Aperture Value: Undefined
ISO Speed Rating: 6400
Focal Length: 35 mm
Lens: Undefined
Metering Mode: Pattern/Matrix
Exposure Time: 1/20 sec[/quote]Maybe you're worrying about something you can't do anything about!
Were they processed with different software at some stage? (I note they were finished with Lightroom.)

... And forget what I said earlier as that doesn't seem to be the problem after all !

If you're paying by credit card the card company are equally responsible should you have an issue (Section 75 of the Consumer Credit Act 1974.) Any company will have issues from time to time, however Bristol Cameras are a high street retailer, not a fly by night web only outfit.
https://uk.trustpilot.com/review/www.bristolcameras.co.uk