The official page and FAQ, dated, showing the specific statement relied on. If the description cannot be pointed to on the official source, treat it as unverified. Keep a copy of what the page said on the day of each payment.
Every claim about the program should be traceable to the official text
Because the framework lives on a government website rather than in a regulation with a Federal Register citation, the only reliable description of it is the page itself as it reads on a given day. An applicant who is told that land counts, that the gift is refundable, that the fee is waived for certain nationalities or that processing bypasses the visa bulletin should ask the person making the claim to show the sentence on the official page or FAQ that says so. If it cannot be shown, the claim is not part of the program.
The same discipline applies to the applicant's own file: save a complete dated copy of the page and FAQ on the day of the application, the day of the fee payment and the day of any gift, together with payment confirmations and vetting correspondence, so that any later change in terms can be measured against what was relied on. A short memorandum noting the carrying immigrant category, the visa-bulletin position and the per-person amounts calculated for the household completes the record. Professional advice should cite the official text rather than replace it.