My understanding (get other opinions) is if you were formally hired and you signed a contract of some kind for the job, or you were on payroll during the training when you washed out, then it was certainly a PRIA-recorded training event in accordance with FAA administrative law, and you must report it to any airline you apply to. However, some airlines circumvent the PRIA start date on purpose by informally hiring new pilots until they pass initial training, because they can use this as a way to entice low-time pilots. In the latter case, I believe you are ok to decide for yourself whether not to report a washout. The ethical side of it is another matter, I am not addressing that topic. You can also find out what your PRIA record looks like using Freedom of Information Act if you do not know, or just call the airline.