Guys, I've had a look at what I have and this is the data gleaned:
Symphony No. 2, digital recording 1982 [double vinyl, also on double CD]
Symphony No. 5 & 10 (Adagio), analogue recording 1979 [double vinyl]
Symphony No. 6, digital recording 1983 [double DMM vinyl]
According to the list on the back, Nos. 3 & 7 are recorded digitally. Nos. 4 and 8 are not mentioned so may be digital as they came later.
This may account for some of the variation in sound quality. I must say all mine sound good on vinyl, and the 2nd on vinyl is appreciably better than the CD.

