Having accumulated a fair number of older pens now, there is a consistent observable experience in their performane: the pen improves steadily over the first few months of writing.
Here is the scenario - buy an older pen (50s to 90s) from ebay. Clean it thoroughly, ink it.
It skips, or had bad flow or is just boring to write with.
After persevering for a month or so, the pen improves its flow, stops skipping and develops a character. The nib ever seems to become softer.
So what is happening in this 'writing in' process for older?
Is the pen shedding microscopic dried ink particles (despite cleaning with flush)?
Is the metal in the nib tempering, changing at a crystalline level?
Does tipping develop oxide over years which gradually wears off during writing?