Rust spots on older leaves, most likely causes ?

[AutoMicroClub]

This is a retrospective issue so no pictures are available, other than in a post I made a while back... you can just about see the rust a bit if you look close... you can just see a few yellow spots that slowly turned dark brown later on.

https://www.thctalk.com/cannabis-for...179763&thumb=1

Trying to work out what may have been the cause..the new small leaves on/in the buds were clawing a bit during this rust spot outbreak. All organic, basic organic veg feed NPK 4-1.5-4 then Biobiz Bloom with some mollasses from week 4... myco innoculated compost.

Was a micro grow 1 Litre pot compost.

Trying not to have those rust spots again. It did not seem to cause any major issues
the plant survived and continued to grow develop trichomes etc. 60pct Sat 40pct Indica Autoflowering strain. Any thoughts welcome.

I did look into it and thought cal/mag (I did add a bit of mineral tablet powder on the soil late on) or a kind of rust spot fungi... never got to the bottom of it. The foresight of a good myco innoculation probably got it through to the finish line.