in April 1968 I flew my Q X-C (Cranfield - (Henlow) - Cambridge - Ipswich - (Henlow) - Cranfield) before my PPL test, so no - it certainly wasn't always the last item flown before a candidate applied for a PPL.
1968 was prior to the introduction of the NFT; (which came about as aresult of candidates getting lost on the QXC) it then became mandatory to have passed the NFT before attempting the QXC. I recall the uproar when the JAA placed the 150 nm XCTY prior to the Skill Test.