It is quite clear that provided the WJR initials are Hamish, then he was inspecting the decks.
We have WJR signatures on the batch of decks with low numbers up to 000095.
At present I have not seen a WJR signature on any of the batch of decks from 000545 upwards. Two have the squiggle signature and the others are either unclear or not shown. The labelling suggests they were originally intended to be sold as Ariston but if Hamish did not actually purchase them he may not have done any inspections for that batch.
My understanding is Ivor was working in Israel from 71 so may not have been around to inspect them. Not clear when he came back to Glasgow. "But in early 1971 he took himself off to Israel and worked initially as a production manager in an engineering company, before setting himself up as an engineering consultant".
https://www.scotsman.com/business/companies/minister-of-sound-who-strikes-the-right-notes-1-1286407
Jack was running a large factory so I doubt if he would be involved with inspection.