these are actually HG13 cells, not PX675. I have a stock of these packs - EXACTLY the same package design!- dating back to the mid 1990s (they were dirt cheap then) and I don´t think they are "real" mercury oxide cells. Their "working life" is much shorter than mercury oxide cells, their voltage output is higher than 1,4V and -what is worse- I had a few leaking in their seals while stored in my fridge, about 2 cells per pack of 10. Real mercury cells rarely ever leak.
Since my stock is depleting fast, I decided to switch over to hearing aid zinc/air cells for 2,50EUR for a blister of 6 cells.
Out of curiosity, I couldn´t find a price on that website you mention - what do they quote for these cells?