The B5094 Nixie was tickling me: why only two symbols light up? Why others don't? I asked around and the hint was to increase the voltage supply (as well as the current limiting resistor).
Worth a try. My PSU module reaches 186 V: not enough to light up other symbols. Then I added in series a 12 V battery pack for a total of 198 V and ... all 3+3 symbols said "Hello!".
The series resistor was increased to 47k that is probably still too low. I need to measure the working current of that specific Nixie and make sure I do not exceed the 3.5 mA stated in the datasheet.
The need for an increased voltage is a sign that the tube is "tired". The 4th B5092 doesn't fire with 198 V. I may try to go higher but that's not too easy to achieve with batteries, or keep it as a souvenir.