Answer from a user with 9 on-site reputation but protect option is not available (in sufficiently old question)

Question

For 15K users protect option is supposed to work as described here:

the question must have at least one answer by a new user aka a user with < 10 rep on the site (which is the required rep limit to answer protected questions)

This answer made me wonder if there is a off-by-one error in calculation somewhere. At the moment of writing this comment its author has only 9 rep on site (6 from one answer and 3 from one question) but protection link isn't displayed to 15K users.

_{I additionally checked that question is more than a day old: per FAQ this is enough for protect option to become available.}

Answer 1

You earn 1 rep just by joining the site. You can never have less than 1 rep. So to have 10 rep, you must net at least 9 points after joining. If you get an association bonus, you'll start at 101, but only have 1 point toward the ability to answer protected questions - so you'll still need to net at least 9 additional points.

The user in question has, after earning 9 points from 1 question and 1 answer, 10 points, and thus can answer protected questions; this also makes their answers ineligible for triggering the ability to protect questions.

The test is as described:

IsRealNewbie(u) => u.ReputationWithoutAssociationBonus < NewUserPrivilege

If true, the test both prevents the user in question from answering a protected question and enables protection on any question where they have answered.

The alternate interpretation (user must net 10 points, for a total reputation of at least 11) would result in a situation where, upon earning the Remove New User Restrictions privilege, a user would still need to earn one more point to actually answer protected questions - so clearly this interpretation is invalid.