Ser vs Ir

Ser vs Ir
 

So the Preterito and the Imperfecto del subjuntivo of Ser and Ir are conjugated the same:hmm::hmm::hmm:

Context is needed to tell the difference. :)

The names you used for the tenses aren't the same names used by all native speakers, so there may be some confusion.
Suffice it to say that the pretérito perfecto simple conjugation of ir and ser is identical and, since the subjunctive equivalent (pretérito perfecto) is formed from the third-person plural of the indicative, it makes perfect sense that both ir and ser share the same conjugation in both places.