Avoid missing attachments in Thunderbird with attachment keywords that you can customize!
Go to Thunderbird Menu > Settings > Composition, and scroll to 'Attachments.' Click on 'Keywords' to maintain YOUR custom keyword list. 📎
If you're, ahem, strategically not attaching documents when you say you've attached them, you can turn reminders off across Thunderbird in Attachment Settings - or disable reminders for the current message when the attachment reminder pops up. 😉