If the ATF checker rejects a valid sign value, this value needs to be added to the ORACC Global Sign List. Email your request to Niek Veldhuis (veldhuis at berkeley dot edu); usually, the value is added the same working day. If you haven't heard within a week, try again.
In your email, report the new value (e.g., reṭ), the sign name (e.g., ŠID), and the sign number in one of the standard sign lists (e.g., MZL486; see the list below). In addition, provide (brief) documentation on the validity of the sign value, including the text you are working on with text name, P number column/line number and transliteration of the word in which the value appears. Use the format in the example below. If there is any discussion of the sign value in MZL or some other publication, it is useful to note that, too.
Sign value: reṭ
Sign: ŠID = MZL486
Attestation: [CT 12 28 = [your project name]:P398345 r ii
10, reṭ-bu] (NB: this is a made-up attestation!)
Documentation: For reṭ MZL refers to riṭ (= ŠID).