Years ago, everyone feared wikis for the illegitimacy. But that dwindled down with moderation and acceptance of generally agreed ideals. Either way, no one should take the Wiki seriously at 'face value'.
Obviously we know as readers and viewers of the series; after Tobirama's reign, Sarutobi stepped in and then Minato. My thought is because they were both Hokage's, Minato might have had access to Tobirama's past files, documents, whatever. He inherited the rank and job Tobirama once held. So maybe through undisclosed doors and events, Minato himself practicioned and fiddled with Tobirama's fuinjutsu. (Albeit Minato himself, has shown a great deal of knowledge in Fuinjutsu, as well as his relation with the Uzumaki's the sealing experts themselves.)
Either way, it could indeed be possible that Minato pirated Tobirama's creation; which is why we have the two custom tags they have. Or he could have just learned it from Tobi, we will honestly and probably never know. But I do like the idea that over years, Minato had replicated the seal in his own method. Still making it Hirashin, although different from Tobirama's. This is what makes each hirashin user's marker different, since we don't exactly know just what the original user has composed into his own seal. Given that Minato couldn't hack into Tobirama's old networks.
Then again this whole reverse engineering thing could get out of hand. Where would it end? What will be the point of the originals? And their secrecy. The list could be endless with 'reverse engineering' a technique. Although, it doesn't have to be out of the question. If by legitimate RP means, your character has come across a way to gain a technique through experimenting and researching; over a lengthy time, then so be it. These teachings shouldn't become instant and should indeed be an over time sorta dealio.
Also just putting this out there since it was mentioned. Being an Uzumaki doesn't make you a sealing expert, but having the blood of an Uzumaki allows you a more advanced knowledge and chakra supply to preform above average seals; simply from my own observation(Nagato/Karin weren't some sorta sealing masters). It is only when you further enhance such ability YOURSELF that you can become an Uzumaki 'sealing expert'. I take pride in my blood and don't wish to see it tainted by you power hungry monsters. >__>'