Re a 56 reg Octavia 2.0 PD TDi purchased s/h in good condition ex fleet late 2009. Came with well-reviewed tyres, front 2 x Michelin Primacy HP w 6mm tread, rear 2x Pirelli P7 with 4-5mm tread, tyres been on 2 yrs done 35k miles. One rear Pirelli punctured at the w/e and put on the spare - a Dunlop SP Sport 01A with 8mm tread. Been used, as muddy, but 8mm tread.

Should I replace both rear tyres to ensure two same (per all vehicle/tyre manufacturer advice) or would that be overkill given the spare had 8mm tread?! Owner's manual says 'Never fit tyres which have already been used without knowing their previous history', but what's the risk? What should I be looking for? The DOT manufacture date was 3306.

Secondly, how much does it matter if replace the other rear tyre with something 'similar' to the Dunlop SP Sport 01A but not exactly the same? None of my local tyre fitters seem to do the Dunlop SP Sport 01A, but there is a Dunlop SP Sport 01.

Apologies if simple/obvious q - newbie to car maintenance, so many thanks for all advice!

Regards