usually you would go through seed funding, the series a,b, and possibly a1 and b1. If you entered c or d territory it meant that you still had a chance but vc would be following you very closely. After d, you could raise money, but it would be under very unfavorable conditions

The number of rounds is irrelevant. Having crunched the data, what is relevant to terms is simply as you'd expect the rate of growth. The only reason it rarely happens with fast growing companies is that the liquidity of an IPO is attractive. As a result, companies doing many rounds are disproportionately companies that are performing too poorly to try and IPO.