I was going to make a post saying "Lucretia told everyone the truth there were seven Grand Relics instead of covering her ass and saying there were six because she's a storyteller, and six sounds objectively less cool than seven," but then I thought about it and actually, if you look at the timeline, I think this was probably a very pragmatic or at least tactically safe decision on her part?

When Lucretia founds the Bureau, Junior hasn't been born yet. Lucretia obviously doesn't even know Junior will be born someday. So once she inoculates Bureau members with Fisher — a necessity to staffing the Bureau in the first place — Lucretia can't keep any more secrets from them, with only one Voidfish at her disposal. And crucially, while Lucretia is the Bureau's primary source of info on the "Red Robes," basically all her recruits lived through the Relic Wars.

Upon inoculation, they'll all presumably remember at least some details about the Grand Relics. Obviously no one but Lucretia would know anywhere near everything about each Relic and their properties, not least of all because of a high eyewitness fatality rate, but part of the reason the wars were so deadly was because word of the Relics spread. Everyone in the world knew a few things about them.

So, if Lucretia were to tell her recruits: "oh, don't worry, there's only six terrible artifacts we need to destroy, tee hee!" then it's very possible that assorted Bureau members — especially Seekers, for whom looking into the Relics is literally their job — could start comparing memories amongst themselves, and put together that there was a seventh, leaving Lucretia with no option but to admit that she lied. If I recall correctly, the podcast never explicitly indicates what/how much damage the Bulwark Staff did to the world — but I find it hard to believe that it didn't do anything an inoculated person could later find record of or remember. (There's an admittedly good fanfic premise, though, in Lucretia leaving her Relic in someone's care to make it stationary, like how Magnus gave the Chalice to Jack, or how Barry is theorized to have given the Bell to the Wonderland twins.)

I digress, but the point is, Lucretia may have necessitated a lot of little lies for her future self by admitting there were seven Relics, but trying to winnow it down to six could've easily bit her in the ass, and she was definitely smart enough to realize that. She acted accordingly at the time.

And by the time Junior comes around, then of course she could theoretically use them to erase the Bulwark Staff from her employees' minds — but by then, she's been hiding the Staff under everyone's noses for about a year, and no one has gotten suspicious. So if it's working, why change it? She's no doubt also smart enough to reserve Junior's power for emergencies only — even if people forget information, they can still retain the feeling they're forgetting something. With people planetside, that's one thing — but with her employees on the moon, from whom she needs unshakeable trust?Probably not worth it.

Overall, a it's deceptively rational decision on Lucretia's part, honestly. And also, seven Grand Relics still sounds way more badass than just six.