Valuation and Headcount are supposed to reflect the valuation and headcount of the company when the offer was received.
These offers with large equity grants (>1%) at very high valuation companies were likely received when the valuations were lower.
I message this on the Add page, and most people follow it. It looks like a few people didn't in the examples you cite.
I need to do a better job of messaging this on the Add page and add validation on the Add page to calculate Valuation * Equity = Dollar Value of Grant.
Let me know if you have other ideas.