From the IRS perspective gold is treated as a collectable, and it is on you to maintain such records however you obtained it. Obviously, a notebook entry rather than a receipt from a business like APMEX (which maintains records of and reports sales) is whatever you put in it at the time you enter it.
A cash sale of your gold is a different issue. But let's say you sell four eagles for 20K in cash. You can now either meter out that cash for items small enough not to attract attention or deposit it. If you deposit it and do not declare it as income, you are asking for an IRS inquiry. Depending on your income, that declaration is likely to cost more in taxes than the 28% on the capital gain. Should your heirs inherit the gold from you, the cost basis clock starts then for them.
By the way, gun collections are treated essentially the same way if inherited. So, if you have a truly valuable collection that will not be used by an heir, the smart move is to not necessarily maintain records of initial acquisition cost, but provide your heirs with the contact information of a smart, knowledgeable appraiser who can provide a generous valuation for each firearm. That establishes the cost basis for let's say your spouse who has no real interest in the collection. The guns go to the right auction, and depending on the grading of the appraiser, your spouse will be left with little in the way of a capital gain, and quite likely can declare a loss.
