The four o'clock problem: IV or IIII?

On the faces of clocks and sundials that use Roman numerals, four o'clock is often denoted as IIII instead of IV, as it should be. Why is that, is a frequently asked question.

A number of excellent websites discuss this question extensively:

Two main points taken from this discussion are:

But how about the year (1742) on the Frenswegen monastery in Germany (between Nordhorn and Ootmarsum)? By the way, Ootmarsum is exceptional, as the clock on the church has IV instead of IIII!

 Frenswegen monastery (Germany)