The Short Answer
Tell the hotel in writing before you arrive, not at check-in. By the time you reach the front desk the arrivals list is set and the good rooms are allocated. An occasion noted on the reservation a week ahead, ideally through a preferred-partner advisor whose note the hotel actually reads, is far more effective than mentioning it at the desk.
Search for how to get upgraded on a honeymoon and you will find the same advice repeated everywhere: mention it at check-in, be nice to the front desk, ask politely. None of it is wrong exactly. It is just aimed at the wrong moment in the process, and it misunderstands who actually makes the decision.
Why mentioning it at check-in is close to useless
By the time you are standing at the desk, the hotel has already run its arrivals report, allocated rooms, and flagged which guests are getting attention that day. The person checking you in is frequently not authorised to reassign a suite on the spot, and on a busy afternoon the inventory that could have been used for an upgrade has already gone to someone whose reservation carried a note days earlier.
This is the actual mechanism behind the advice you have read. The people recommending you mention your anniversary at check-in are describing something that occasionally works. What reliably works is the same information arriving early enough for someone to act on it.
What the hotel actually needs, and when
Three things, in writing, roughly a week before arrival: what the occasion is, which night it falls on, and anything specific that would matter, a quiet room, a particular view, a dietary restriction for a celebration dinner. A hotel that receives this a week out has time to route it to the right department. The same message at 3pm on arrival day reaches someone with no room left to manoeuvre.
Where a preferred-partner booking changes the outcome
Anyone can email a hotel before arrival, and it is worth doing. The difference with a preferred-partner booking is whose message it is. A note attached to a reservation from an advisor the property has an ongoing commercial relationship with reaches a different inbox than a guest's own email to a general reservations address, and it arrives alongside amenities the hotel has already agreed to extend, breakfast, a credit, upgrade priority.
That is not because the guest matters less. It is because the hotel has a standing interest in that advisor continuing to send it business, and a note from that channel carries an implicit account relationship behind it. The practical result is that occasion requests made this way get actioned more often.
An occasion is the single most useful thing you can tell a hotel in advance, and the single most commonly wasted piece of information, because most guests save it for the check-in desk where it has the least power to change anything.
What genuinely improves your odds, beyond the occasion itself
Occasion aside, three structural factors do more for upgrade likelihood than any amount of charm at the desk. Length of stay: a hotel has more room to move on a four-night booking than a one-night stay, and more incentive, since a longer stay means more on-property spend. Timing: midweek and shoulder-season arrivals leave surplus premium inventory that the hotel cannot otherwise sell. And room category booked: an upgrade from a base category has more rungs above it than one from an already-elevated room.
None of this is manipulable on a sold-out Saturday in peak season, at any hotel, through any channel. As we have written elsewhere, "subject to availability" is a real constraint, not a formality, and any advisor promising you a specific suite on a full night is overselling.
The honest limits
An occasion noted in advance reliably produces recognition. It does not reliably produce a suite. What it produces, in our experience, is a room in a better position rather than a better category, an acknowledgment on arrival, something sent up on the night itself, or a table held at a restaurant that was otherwise full. Those are the realistic outcomes, and they are worth arranging properly. Treat anyone guaranteeing more than that with suspicion.
Our position
If the trip matters, say so in writing, early, through whichever channel the hotel is most likely to act on. That is the entire technique. The advice to mention it at the desk is not wrong so much as late, and lateness is precisely what costs you the room that was still unallocated a week earlier.