There's a German idiom "turning an X into a U" (U being a V) with the origin about changing the number on a chalkboard recording your purchases in a pub. In a hand-written contract you can do the opposite, adding two lines to turn a V into an X.
More generally, a fun fact many miss about Roman numerals is that you can do this with all digits (except I because that would require fractions):
X (10) -> V (5)
C (100) -> L (50)
M (1000) -> D (500)
It's less obvious in prose like this but it helps if you consider that these numbers would normally be drawn with straight lines (e.g. M would often end up looking more like |X| instead of |V|, which explains why cutting it in half would result in |> or D). This is also a handy way of remembering the less frequently used digits like L or D which are harder to remember because they don't really stand for anything (unlike C = centum and M = mille).
If something ends with “I“ you can add two more I’s and have it go from 1 to 3.
And so on.
Using that appending technique works to sneak the year forward in most cases - perhaps that was the intended benefit? We can update the copyright from (say) 1950 to 1951 without any obvious tampering.
