I've used various nos quads on my pair of Rachel's purporting to be matched but within a small parameter ( when you read the figures they are not equal )and what happens is that you notice the meters will show a small difference ; one slightly higher and one slightly under the the ' target' of what the tubes should be as 'new' I say target because one is above and one slightly below as if balancing each other. This will happen on each amp. The sound has always been perfectly balanced between the speakers, which I take to mean as ithe description of self biasing.
At the moment I have all meters reading 40, which is a fluke for me but may be normal for those that buy new tubes ( really new ).