I've got a query or two out, awaiting answers from people more knowledgeable about Sheaffer history than I. Having said that, I am fairly certain that the Skrip-well bottle came out as early as sometime in the 1930's, and in any event I am confident it preceded the introduction of the Snorkel (as well as remaining in production after the Snorkels were discontinued. So, if it goes back, the larger OS Balances would have still be in the catalog.
That is entirely possible. I'm just quoting what that particular box said. I probably know even less about Sheaffer history than you, so I don't know at what point that particular style bottle (or box) came in. I was just kinda amused by the advertising, so I'm presuming the yellow boxes are from the 1950s. I have another bottle that came in a red box that also has the reservoir in it. I gather from what I've read on other threads that those are more recent (1980s I think someone said) than the yellow boxes (and oddly, it says "Sheaffer" but not "Skrip" on either the box or label).
Although given the design, I'm wondering if the reservoir was for smaller pens and nibs, and you used the main part of the bottle's mouth for large pens (my mother-in-law recently gave me what may have been her father's pen, which knowledgeable people on here have told me is a Balance Oversize. It's got a Lifetime nib, but I'm not sure what the size of it is (I'm guessing at least a #6, maybe a #8).
Ruth Morrisson aka inkstainedruth
"It's very nice, but frankly, when I signed that list for a P-51, what I had in mind was a fountain pen."