Here's a possible explanation as to how he ended up with millions in an IRA account...from the same Vanity Fair article.
Mysteries also arise when one looks at Romney’s individual retirement account at Bain Capital. When Romney was there, from 1984 to 1999, taxpayers were allowed to put just $2,000 per year into an I.R.A., and $30,000 annually into a different kind of plan he may have used. Given these annual contribution ceilings, how can his I.R.A. possibly contain up to $102 million, as his financial disclosures now suggest?
The Romneys won’t say, but Mark Maremont, writing in The Wall Street Journal, uncovered a likely explanation. When Bain Capital bought companies, it would create two classes of shares, named A and L. The A shares were risky common shares, to which they would assign a very low value. The L shares were preferred shares, paying a high dividend but with the payoff frozen, and most of the value was assigned to them. Bain employees would then put the exciting A shares in their I.R.A. accounts, where they grew tax-free. With all the risk of the deal, the A shares stood to gain a lot or collapse. But if the deal succeeded, the springing value could be stunning: Bain employees saw their A shares from one particularly fruitful deal grow 583-fold, 16 times faster than the underlying stock.
The Romneys won’t tell us how, or even if, they assigned super-low values to the A shares, but there are a couple of ways to do it. One is to use standard options models to price the shares—then feed inappropriate assumptions into those models. Romney could alternatively have used a model called liquidation valuation, which Kleinbard says would have been “completely inappropriate.” Without seeing the assumptions used on Romney’s tax returns from the years when those lowball A shares were squirted into his I.R.A., we cannot know how he did it. Whatever methods he used, however, the valuations were, according to Andrew Smith, of Houlihan Capital in Chicago, “pushing the envelope.” (Andrea Saul retorts, “Why should successful investments be criticized?”)