Do tubes always need to be matched?

[Ascension]

Thats why its important to have a tube vendor you trust.

Bingo! For power tubes i always buy at least a matched pair if not a quad for an amp that runs a pair so I have spares. Key to not seeing bias drift is to buy from a reputable vendor who not only matches but also burns in tubes. Unless a amp has individual bias pots for each tube it's the only way to get a proper bias. It's much more critical in particular if you have an amp with a fixed bias like many Boogies and Carvins for examples.
Tube amp audiophiles in particular are really picky on this because of crossover distortion. It's not expensive to buy matched sets of power tubes only a couple bucks more most of the time so just makes sense.