If I ask you to take one page that you have printed and demonstrate its valid dates, can you do it.Can you do the same with the sectional you went out and bought without unfolding it? After all, that's pretty much the equivalent scenario with a commercial sectional product, right? (I'm assuming "printing your own" means you didn't find a way to print the sectionals on a true single-sheet, sectional-size piece of paper.)
Even if you can't prove the self-printed chart is current... why would that matter? Unless you actually had outdated charts and the use of those charts was determined to have been a contributing factor in an incident, there's no requirement to prove that you have valid/updated charts.
"You can carry old charts in your aircraft." "It is not FAA policy to violate anyone for having outdated charts in the aircraft." (Source: What is the FAA policy for carrying current charts?)
EDIT: Likewise, none of the CFRs I could find (which really don't even apply to private pilots flying small GA craft anyway) regulated the source of the charts in any way that I could discern.