Don't worry about it, if it's only a max supply change then my suggestion won't be necessary. Without a reward halving schedule I would go as far as saying there is not much point in changing anything as it will erode confidence in the supply changing whenever it suits the community.
My suggestion is the right thing to do as it can be argued this is where the coins supply should be in relation to it's total supply when the coin was started.

Changes:
760 million total supply
3rd April 2022 or close to it the reward halves to 80 for 4 years. This change brings it close to where the coin would of been if no changes were ever made from the start of the coins inception.
840 960 blocks later (year 2026) the reward halves to 40.
840 960 blocks later (year 2030) the reward halves to 20. Gulden will be close to 90% mined out when this drop occurs and most of you will be alive to see it

The 4 year cycle also gives the market time to adjust to the changes and no sudden drop off from 160 reward to 0 when the new max is achieved.

I was one of the few voices at the start who was against the reward change from 1000 to 100 and when they went ahead with the change Rijk never adjusted the max supply to compensate. Next year if the rewards remained the same with the 4 year halving schedule, 75% of the total supply would of been mined out.

Next year Gulden will only have 35% of the total supply mined out and a long way to go before 75% is achieved. This scares off investors.

To correct the situation the total supply needs to be adjusted to where current supply is 75% and a reward halving introduced on the 3rd April 2022 when the next reward halving was expected to take place.

Someone else in the team or community can work it out but the max supply will need to be adjusted close to 760 million to bring the initial reward structure back into balance with a reward halving starting on 3rd April 2022 and every 4 years after.