Yeah this is an interesting question! As you’ve pointed out, from what we know about viewing multiple Pensieve memories (which, granted, we only see twice in the series), I’m inclined to say the other two must have come temporally after SWM.
I’m assuming Dumbledore had granted Snape use of the Pensieve to ensure that Voldemort, through Harry, will not discern something that puts Snape at risk. Therefore, I believe the other two memories are memories that would be utterly damning, that Snape would not be able to “spin” if Harry/Voldemort were to see them, which are:
1. Snape going to Dumbledore on the hilltop and promising him “anything” (this contradicts the story he’s been telIing Voldemort and the DEs, that Dumbledore took him on only after Voldemort’s defeat, when he spun a tale of “deepest remorse” of his DE days)
2. His agreeing to protect Harry in memory of Lily (Voldemort doesn’t think Snape truly loved Lily, and seems like he hadn’t heard about her in years, and doesn’t think she was part of his “tale of remorse” that he spun to Dumbledore. I think Snape would loathe anything about their true relationship being known to Voldemort, so I think this probably contradicts whatever Voldemort think he said to Dumbledore to convince him to trust him.)
So in this way, I actually think SWM is the anomaly here. I think Snape’s choice of depositing this one in the Pensieve is not necessarily for his or the Order’s operational security like the other two are—he could easily spin it if necessary—but out of an overwhelming sense of shame alone. To have Harry see his greatest shame (seeing, with Lily’s eyes, mind you), to have Harry see him choose to intentionally hurt the girl who was the best part of his life…completely intolerable for him. This isn’t an unintentional or uninformed or abstract harm like his handing over the prophecy, which I think he could count on Harry not understanding anyway. This isn’t the slow-dawning realization or a grapple with his conscience, but something that he can and does perceive as an inflection point for him.
That makes Harry’s seeing this one in some ways all the worse, given it’s the only one he put in there specifically so Harry wouldn’t see it. But I always felt like Snape’s anger when he pulls Harry out of the Pensieve isn’t just fueled by shame, but the type of anger one feels when you narrowly avoid a fatal mishap. He’s shaking and pale; there seems to be an undercurrent of fear here. So I believe that Snape arrived only just in time before Harry/Voldemort saw something truly catastrophic to Snape and the Order.
This is also why I believe Dumbledore let Snape give up Occlumency as a bad job. It was too dangerous to continue. The tenuous trust they had reached between them collapsed spectacularly, and now not just Harry but the Order is in danger. Better to revert to standard operating procedure and keep an eye on Harry at Hogwarts, especially with resources stretching thin at the castle.