What should be used in place of "cf" for references for counterfeits?

For example: N#207304

The reference line is: References  Hartill# cf. 22.7, FD# cf. 2174

The cf is used to identify coins that should be compared against the counterfeit images, but “cf” isn't in the list of abbreviations approved for use on Numista.

https://en.numista.com/catalogue/contributions/abbreviations.php

What should be used instead? Would “References  Hartill# 22.7(compare), FD# 2174(compare)” be understandable?

I'd rather not use the reference field for such case and add in the comment section a brief note like “counterfeit of Hartill# xyz”, or "for genuine coin, see Hartill# xyz".

And keep the link to the original coin in the "see also" section.

Wow, there are lots of bogus references under exonumia (beyond the cf I found earlier). (And many correct KM references as well.)

Some are easy to fix – I just converted a bunch of KM# 99999 references to TC# 99999 (after checking each on tokencatalog.com).