When I open a note and delete an item from a numbered list, the list numbering doesn't update in the edit version of the note (the view version is correct), and just skips the index of the deleted item. The last number in my list is 24 in view mode, but 28 in edit mode because some indexes were skipped.
Joplin uses Markdown at its core for formatting notes. Markdown basically ignores the number (see exception below) so you could use all 1's or any random sequence. When the Markdown is rendered the list will be correctly numbered.
Personally I enter all numbered lists as:
1. item
1. item
1. item
which displays as
item
item
item
The exception is the first number. The renderer will count on FROM that number and ignore whatever is typed after so
77. item
65. item
2. item
displays as
item
item
item
This lets you manually "resume" lists broken by a line of text inbetween.