I mean... It could just as easily be that TARDIS is both the singular and plural form. Like sheep or fish.
The jokester in me wants to say TARDIS → TARDES by analogy of penis → penes but the fact of the matter is that Time and Relative Dimensions in Space doesn't really pluralize even when it isn't abbreviated
I mean... It could just as easily be that TARDIS is both the singular and plural form. Like sheep or fish.