A printed catalogue shows a price, and a handwritten number sits beside it. The temptation is to call the second figure a correction. That may be possible, but the marks alone do not yet tell you who wrote it, when, or for what purpose.
Separate the printed entry from the addition
Transcribe the printed price and the handwritten note in different fields. Describe where the addition appears and whether the original has been crossed out. If you are working from a scan, say so rather than claim to have examined the paper or ink.
For an invented example, a printed 12 with a handwritten 10 beside it establishes two visible figures. It does not establish a sale, a discount, or a new official price list without further evidence.
Look for a pattern across the copy
Are similar additions present elsewhere? Do they use comparable placement or wording? Record the pattern without assuming that matching-looking handwriting proves a single author. A note on the cover or an archive description may offer context worth checking.
Our article on reading a catalogue's selling unit still applies. Before comparing the two numbers, confirm whether they refer to the same quantity and product variant.
Keep the copy’s history visible
A marked catalogue is a particular copy with a history of use. Its additions should not be silently transferred into a transcription of the publication as if they appeared in every printed version.
A careful description might identify an undated handwritten figure next to a printed price and leave its purpose open. That wording preserves the interesting evidence while giving later research room to explain it. The annotation becomes a question to investigate rather than an answer supplied by guesswork.