Triode Naming Convention

The question is simple: When it comes to schematics e.g. I see V1A and V1B How do I know which triode this refers to is V1A Pins 123 and V1B 678. Most data sheets indicate pins 123 to triode two and pins 678 to triode 1

In the Philips data sheet for a 12AX7 they even have a remark stating pins 678 or triode 1 is a better triode with regard to hum.

Some schematics actually show the pins for the specific triode but most only show V1A V2B V3B etc. Its obviously most critical in the first pre-amp stage unless there is a reason by the designer to have something a little different.

Can anyone explain this convention or lack there of?

Thank you
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