Here are several photos I took yesterday of I-99 signage on US 15 in New York between I-86 and the Pennsylvania border.

This lone I-99 route marker is on the northbound freeway north of exit 8 (NY 417).

A closeup of that route marker. None of the ones I saw had the state name.

A sign assembly on eastbound NY 417, approaching the ramp to northbound I-99/US 15.

South of exit 11 (another junction with NY 417), the I-99 marker is paired with the old US 15 marker.

An I-99 reference marker, southbound on the newest segment of the freeway south of exit 6 (junction with a county route). I saw I-99 reference markers on the older segments (like under the sign shown above south of exit 11), but I don't know for sure that all the US 15 reference markers are gone, and vaguely recall seeing at least one of them.

Here's one of the two End I-99 markers at the south end of I-99 in New York (the other marker is on the other side of the southbound lanes). The "Pennsylvania Welcomes You" sign in the background confirms the location. I didn't see any End I-99 markers at the north end of I-99 at the I-86 junction, but maybe they were on the ramp I didn't take.
I also didn't see any I-99 signage on I-86 eastbound. The BGSes approaching the I-99 junction still refer only to US 15.