Can 上 always be used like English ” ” (i.e.: same as above)?
According to this kknews article (找薦004.疊字符/重字符這麼用，有沒有錯？), many variants were used for the iteration marks, including marks that were or looked like the following:


「S」
「々」
「匕」
「上」
「乙」
「=」


It goes on to state that what looks like「匕」is normally thought of as a result of rapid writing leading to graphical corruption, or degradation of the engraving medium (for steles). We know that「々」came from a variant of「同」, but the origin of「=」is conjecture without any hard evidence. It may be later surmised as「上」or「二」, but it is probably impossible to ever know.

BTW, if you search your copy of 躋春臺, it will have more examples of「匕」as the iteration mark.