The additional fields provided by jabref should be defined in a datamodel for biber, which is provided by jabref, or be included in the upstream biber or maybe even biblatex project.
for example source and timestamp
this would suppress annoying warnings and there surely will be usecases, like grouping all citations from crossref or showing the citations in order of finding them
Biblatex is open-source as well, so you can add any missing field definitions yourself. https://github.com/plk/biblatex
i suggested it there and it will only be implemented, if there is enough request for it.
In the other hand it would be usefull to provide a jabref conf for format checking etc like described here.
The patch is more or less two lines for field to add (if only using them as bare literal fields) and it could probably be rebased on the currentversion of biblatex
$ diff -c /var/tmp/par-6a656e73/cache-c42f71badd0560e4ca20f1f2f69f6d02d89bae43/inc/lib/Biber/biber-tool.conf biber-tool.conf
*** /var/tmp/par-6a656e73/cache-c42f71badd0560e4ca20f1f2f69f6d02d89bae43/inc/lib/Biber/biber-tool.conf Wed Jul 17 13:13:21 2019
--- biber-tool.conf Thu Jul 25 20:57:53 2019
***************
*** 474,479 ****
--- 474,480 ----
<field fieldtype="field" datatype="literal">abstract</field>
<field fieldtype="field" datatype="literal">addendum</field>
<field fieldtype="field" datatype="literal">annotation</field>
+ <field fieldtype="field" datatype="literal">timestamp</field>
<field fieldtype="field" datatype="literal">booksubtitle</field>
<field fieldtype="field" datatype="literal">booktitle</field>
<field fieldtype="field" datatype="literal">booktitleaddon</field>
***************
*** 615,620 ****
--- 616,622 ----
<entryfields>
<field>abstract</field>
<field>annotation</field>
+ <field>timestamp</field>
<field>authortype</field>
<field>bookpagination</field>
<field>crossref</field>
another option would be to add a local config like here