The trick to getting full credit for you charitable deduction is to get the charity’s acknowledgment for your gift at the same time they receive it. The acknowledgment must be given in a timely manner for the gift to be deductible. So say I.R.S. and the Tax Court.
Keep in mind this requirement has nothing to do with how honest and legitimate the charitable gift is. It really seems like an unfair regulation. On the other hand nobody ever said that taxes were fair.
The basis for the rule is an effort to prevent tax payer fraud. It’s too easy to claim a charitable deduction when none has been made, and then seek out some charity to give an acknowledgement receipt. It becomes more difficult when the “charity” has to prove the date the donation was made as the receipts are numbered in sequence. It tends to keep the tax payers honest.