I wanted to check that all the numbers on all the tubes were working fine, so rigged up each digit on each of the six tubes in turn.

Thankfully, all the digits are operational - but that should be the case seeing as these are 'old new stock' aka old but never used. One thing that dawned on me during the first couple of Nixies, was I hadn't connected a current limiting resistor. D'oh! Hope I'd not shortened the lifetime too much, so reckoned on a 1k resistor based on an example circuit diagram that I'd been referencing. You'll notice a lack of this resistor in the above picture.

It also seems that 1k is minimal and 15k is more the norm when a Nixie is connected directly to a ~170 volt supply. Oops! :/ At least I was playing it safe as possible whilst running through all these tests...