Just like public companies, pre-IPO company value fluctuates over time. Hopefully, the value and share prices are increasing over time, but they may also decrease. The overall value is driven by company assets and liabilities, revenue, earnings, etc. Additionally, in pre-IPO companies, there is negotiation with major shareholders when a price of a round is set. Therefore, depending on the point in time at which shares are purchased (or the round in which shareholders are participating) people will purchase shares at different prices. I don't think per IPO market is overvalued.