Look, as long as you presure cook your jars long enough they should not contaminate because of environmental factors... dirty house etc... this only starts biteing you when you actualy birth the jars...
So, if jars are well sterilised but still contaminate, you are introducing the contaminants by way of the spore syringe. If you properly flamed the needle red hot between doing each jar, only a few should get contaminated from a bad syringe. This is also why I advise people to use as little spore solution as they can, and give it a few days to see if it takes. The less stuff you inject into a sterile jar, the less chance for contamination.
Try to inject it so that the spore water runs down the side of the glass, if it starts growing in the centre of the grain mass you won't see anything until its grown to the side...If you get the spores on the outside close to the glass you can see when it takes off.
I'm waiting on some jars to cool down now, got 4 diffirent strains of cloned liquid mycelium cultre ready in syringes. Remember to write the date of your innoculation on the jar, its easy to loose track of time. Oh, yeah and plan to start your second batch 3 weeks from the first, or you are gonna live with people presuring you to provide more... and haveing to wait 6 weeks again. What you could do is when you birth you jars, keep one back and use for grain to grain transfer into the second set of jars at week 3.