It appears that in August 1942 7RWK became a draft-finding unit--i.e. remaining in the UK as non-operational and providing reinforcements. Unless he was an essential part of the training or admin, it's very possible he could have been sent elsewhere between 5/10/42 and 6/4/45. Do you have a full list of his units and dates from enlistment/conscription to discharge? If not, I strongly encourage you to apply for his service records (see post 4 of this thread).
Here's the explanation for the 7RWK>6RWK moves in '42: 6RWK's next move is to Algeria in Nov '42. Edit: More later. For us Non-GMT people it's silly o' clock.