Could this be it?  From the WSJT-x manual:  (the formatting didn't copy)

12. Decoder Notes 12.1. AP Decoding The WSJT-X decoders for FST4, FT4, FT8, JT65, and Q65 include procedures that use naturally accumulating information during a minimal QSO. This a priori (AP) information increases sensitivity of the decoder by up to 4 dB, at the cost of a slightly higher rate of false decodes. AP is optional in FT8 and JT65, but is always enabled for Q65 and for FT4 and FST4 when decode depth is Normal or Deep. For example: when you decide to answer a CQ, you already know your own callsign and that of your potential QSO partner. The software therefore “knows” what might be expected for at least 57 message bits (28 for each of two callsigns, one or more for message type) in the next received message. The decoder’s task is thus reduced to determining the remaining 15 bits of the message and ensuring that the resulting solution is reliable. AP decoding starts by setting AP bits to the hypothesized values, as if they had been received correctly. We then determine whether the remaining message and parity bits are consistent with the hypothesized AP bits, with a specified level of confidence. Successful AP decodes are labeled with an end-of-line indicator of the form aP , where P is one of the single-digit AP decoding types listed in Table 1. For example, a2 indicates that the successful decode used MyCall as hypothetically known information. Type a7 , used only in FT8 mode, uses information from the previous Rx sequence. Table 1. FST4, FT4, and FT8 AP information types aP Message components a1 CQ ? ? a2 MyCall ? ? a3 MyCall DxCall ? a4 MyCall DxCall RRR a5 MyCall DxCall 73 a6 MyCall DxCall RR73 a7 (Call_1 or CQ) Call_2 ? If a codeword is found that is judged to have high (but not overwhelmingly high) probability of being correct, a ? character is appended when the decoded message is displayed. To avoid misleading spots of occasional false decodes, messages so marked are not forwarded to PSK Reporter (https://pskreporter.info/pskmap.html). Table 2 lists the six possible QSO states that are tracked by the WSJT-X auto-sequencer, along with the type of AP decoding that would be attempted in each state in FT4 or FT8. The FST4 table (not shown) is the same except that it omits the decoding attempts for AP types 4 and 5 to save time. Table 2. FT4 and FT8 AP decoding types for each QSO state State AP type CALLING STN 2, 3 REPORT 2, 3 ROGER_REPORT 3, 4, 5, 6 ROGERS 3, 4, 5, 6 SIGNOFF 3, 1, 2 CALLING CQ 1, 2 Decoding with a priori information behaves slightly differently in JT65. Some details are provided in Tables 3 and 4. Table 3. JT65 AP information type

George K2DM