Nah, don't buy it. If the marines caught wind of her and she managed to slip away every time, then surely the Yonko and even the Revolutionaries would have picked up on her. She had a public bounty and I'm sure the reason why was known to the higher ups in various organizations illegal and non.
Just seems too convenient, but like I said, I'm sure it's going to be explained (at least the Yonko part) soon.
Carrot is the only surprise, coloring-wise. Thought she'd be dark grey or something. Otherwise pretty rad, surprised they didn't put Jack on there but I'll bet he'll be on the next one.
Like I said, when Robin first met the Revolutionaries they told her that they had been searching for her for a long time but had no idea she was working with Crocodile. The Revolutionary basically apologized for not being able to help her in life sooner.
As for the Emperors both White Beard and Shank's wouldn't be after her and now we know that Kaidou has been targeting Wano for the very same information that Robin could give. He is stationed in the New World after all, he has bigger things to deal with. It's no different than the big wigs in the Marines not doing more to help Nami's little village.
Then with Big Mom, who knows? Like with Doflamingo, getting info on people of interest is one thing, but sending pirates out through the different Blues and 1st half of the Grand Line to find one tiny crew in all the ocean can't be easy. Especially not when it came to the Straw Hats. By the time the rest of the world would have known Robin was in the crew the Straw Hats had completely destroyed Enies Lobby and smarter guys like Doflamingo knew it was Luffy who took out Crocodile. They aren't a crew that you go after carelessly.
-Story wise we have a reason why the revolutionaries had not come from Robin, they tried to find her but could not.
-Two War Lords were after the information that Robin possessed. 1 employed Robin, while the other went directly to the Poneglyph source.
- 2 of the 4 Emperors aren't trying to find One Piece.
- The 3rd of the 4 Emperors also went for the Poneglyph source at Wano.
- Big Mom, we don't have a direct answer for but geographically it makes sense that she didn't get involved with Robin yet. We don't even know if she ever had an interest in finding Robin.
- It's not as if Enies Lobby or Alabasta didn't happen, the events completely revolved around major players in the world and what they wanted out of Robin.
I don't think anything needs to be explained in the story that isn't already a given.