A relative of mine gives testimony in a pension case. Most everything she has to say is confirmed from other records and actually her memory for being nearly 70 years old in 1918 and having moved dozens of times is really good.
One problem. She forgot her remarriage to her husband--despite the fact that she remembered her five other marriages. Reading through all the information made it clear she had NOT forgot about her marriage. There was no apparent divorce from this husband and mentioning the marriage would have created more problems for her application.
There's always the chance that your ancestor had a reason for being less than entirely candid.