Just looked at the article on Andrew "Jupie" Mitchell in the "Hub" booklet. It states he rejoined Caley in 1949 after being demobbed and won the qualifying cup and then played for the four following seasons where he won several medals (2 more Qualifying Cup medals, 2 North Cup medals, two League Championship medals, a Highland League Cup medal and a Charity Cup medal) so he was at Telford Street for 1948/49(part), 49/50, 50/51, 51/52, and 52/53.
He won the Inverness Cup and was a runner-up in the Qualifying Cup with Thistle in 1953/54 so the earliest the Thistle photo could have been taken is 1953.
I have checked again the Nairn County photo and it is 1955/56 (taken before the game against Nairn at Kingsmills which ended 11-0 and Mitchell scored four) and 9 of the 11 in that photo are the same as the one above that is listed as 1951/52.