Ray, Peter is probably the best one to post on this, but subject to his clarification; there is no consistency on the Trials rifles, nor on early Holland & Holland conversions on the body wall 'T'. They started to appear consistently during the 1943 run of production rifles. However, I gather the instruction to armourers was that rifles should be stamped with a letter 'T' to denote their 'telescope rifle' status, so where this had not already been done (ie on the early rifles), as they came in to ordnance, the T was often added after the event. This does seem to have been a somewhat variable occurrence though, & so you will see some 'no-T', some 'standard t', & some 'variant T' rifles. Where I say 'variant T' I simply mean that the armourer would have used any suitable letter stamp, whether it happened to be of the same font & size as that used at Holland & Hollands or not. For example I own two BSA 1943 rifles that are perfectly correct, but the side wall T's are smaller than the usual - perhaps they went through the same armourer's hands??!!
Hope this helps.
ATB.