I'm pretty sure all the people who sent their DeBuNe assets back to your account from September 2017 to November/December 2017 didn't make it just to burn their tokens

since that was the time period you set for the swap.
I can see now that almost all of them attached a message to the Asset transfer transaction, either attaching their ERC20 address or either pointing out that they didn't want to use Ethereum.
Some of them were encrypted messages, some of them not, some of them were prunable messages, some of them weren't prunable... but still when using an
archival node you are able to read the prunned ones. You can even see the prunned messages entering the transaction ID on nxtportal.org
So the most of the times, the reason why I wasn't seeing any messages attached to the asset transfer is because the message was prunned. But it can be retrieved using an archival node.

The above are just examples of some DeBuNe asset transfers to NXT-GQ27-DD53-YM6K-ER6HK by that period of time
Please check this, because you are missing out some of your early investors
There were some instructions in the first page of this thread https://nxtforum.org/debune/erc20-debune-tokens-swap/
NOTICE FOR THOSE THAT DON'T WANT TO USE ERC20 / ETHEREUM. Update:
A) Some of you have contacted me asking how to avoid the swap with the ERC20 tokens and swap directly with the DeBuNe blockchain tokens.
...
Case A) I am open to this possibility, and I apologise for not thinking about it beforehand. In this case return the AE token from an Nxt account you will be able to use in the future to send me the DeBuNe blockchain account where I will send the matching DBN.
I can see there are some accounts which transfered back the DeBuNe assets to NXT-GQ27-DD53-YM6K-ER6HK without attaching any message with the ERC20 account in the attached message, so I believe all of them didn't want to go through the Ethereum step for the swap...
They may have contacted me directly, or just wanted to burn their assets. For sure a couple of people contacted me personally, so had no need to put messages there.
R