The tables provided in FCL/amc/gm are for DIRECT VALIDATION although the ppl/ir reference is wrongly understood by Hungarian CAA at least (the 100hrs under IFR crap, if PPL newbie wants to conver IR)
They include guidance for when NAAs want to hand out 12mth max papers for normally experienced crew, to 'cut the crap' of the atpl exams, courses, flight tests. Sadly not doable for majority of pilots moving to Europe.
Cap804 nowadays MOSTLY regurgitates Part.FCL and expands on differences as valid in the UK. I'll try to find the separate doc, but I didn't save it other than on laptop I'd be near in two weeks. Even then, it's UK CAA doc and file or link was from another website.
Your easa reference for converting overseas rating/licence/cert is Article 8, clause 2 and 3. Very very vague. As assessed/recommended by ATO and approved by CAA. Could be cuppa tea and flight test, could be 10, 20, whatnot hours.
The table that figures in separate UK CAA doc, as mentioned, is load shedding exercise, to have less busy staff approving individual requests every case every rating every time. UK is busy with many foreigners converting there due to English, perceived 'value' of overpriced VAT burdened rates and UK CAA admin fees, to have licence from there.
For example in JARs, there was the 15hr IR conversion in same category spelled out. Now it's not. But common practice is at least 15hr training, for which the school and candidate do NOT require individual approval. They may get one for less, but needs to be done specifically with CAA.
Except most of my Part66 passes, I only have FRTOL and theory classes for atpl/h/a and don't see point spending few thousand more just for paperwork and some stuff 30-70% more flying wise.. But that's just me.
Honestly, I wasn't aware of this reduced theory conversion for VFR cpl, may have tried to do that year ago for converting FI(h), but atpl makes more sense as long term back up.. And fixed wing IR covers theory credit for full heli ATPL without self-funded MEIR (H) like lemming..