The segments notes for episode 256 of Sesame Street mentioned Carla Pinza as Maria. So was there another Maria before Sonia Manzano? Or was this a different character? Either way would make sense, honestly. And for the record, there are articles out there mentioning (albeit briefly) Miss Pinza's involvement with Sesame Street. Apparently, she and Raul Julia were good friends.
It's one of those murky areas since we don't have access to the actual episodes to compare. See Episode 0234 which links to that Maria as if it's the one we know now played by Sonia Manzano (our tracking of her as a cast member for that season seems to be based on references in the archgives to the name Maria, not to anything tied to her specifically). But the talk page discusses it, and the archives only said it was an "adult female," no performer name. Apparently in 2010, a user added the Maria as debuting then because "The Maria that appears in Episode 0234 is likely the Maria we all know." So no real evidence. But if it was just a handful of appearances, it seems like it was probably the same name for a different character.
Shane found the Carla Pinza ID more recently, in 2014, so he might be able to weigh in. I thought of checking Playbill.com's vault (they have bios from opening night of a ton of Broadway shows), but her only Broadway credit was 1968, predating Sesame Street.
So, the evidence we have, and fairly slim, boils down to this: Episode 0234 (from CTW archives) and Episode 0256 (from TV Guide) both have a Spanish speaking character called Maria. TV Guide ID's Carla Pinza, and so far there's nothing to indicate Sonia Manzano was involved that season (it was someone's assumption based on character name).
That seems to be it. The articles mentioning Pinza and the show say she appeared, not that she was a regular (the NY Times theater review says she "appears" as if it's a current or recent event, is dated April 25, 1971, and Ep. 0234, the first we have for "Maria," aired April 1st). The date on the NY Times is strong evidence it was Pinza as Maria in both episodes. I'm still inclined to suspect they're basically two different characters (maybe one was the prototype for the other), but we have no visuals or scripts to really judge.
So right now, Carla Pinza definitely should count at least as a Sesame Street guest star (she has some NY TV credits, including a Law & Order, stage, and photos can be found, just not of her Sesame role). If we find out she was used more than two or three times (possible, given vague wording in those articles mentioning Pinza, and since as noted Larry Block as Tom got an uncredited try-out that season), or if this really *was* the same Maria character, we can rework. Some statements and citing of the only sources we have (CTW archive document, TV Guide listing) would be needed. And I'd personally just add Pinza as a guest star to the Season 2 page and either take out Sonia Manzano and Maria entirely, or rework it as a trivia note: "Carla Pinza plays a character named Maria, who from print sources appeared in two episodes. Any relation to the longer-running Maria character is currently unclear."