Qualification is the hard part
Signature requirements are usually expressed as a percentage of votes cast in a recent statewide election, which means the threshold moves with turnout. Many states add a distribution requirement — signatures must come from a minimum number of counties or districts — specifically to prevent a measure qualifying on the strength of one metropolitan area.
Signatures are validated by sampling or full check, and rejection rates are high. Proponents routinely gather well above the threshold because a substantial share will be struck for duplicate entries, unregistered signers, or mismatched addresses.