thanks a lot for the manual verification. I'm sure this took some time and I really appreciate. I just tried to follow about the 400 ASA @ 16 mins and I found you are right as long as I strictly follow the specification. However, as soon as I adapt the contrast to my enlarger or scanner, the normal EI needs to be adapted.
Regarding batch variations, I think it's a good idea trying to keep track by occasionally mixing some test sheet into regular film processing and adjust curves accordingly, if required. Next to batch variations in film production, I guess other components like developer and fixer are subject of batch variations as well, not to mention the water as the very basic.
Thanks again for your support.