py-jmespath: Unknown flavor 'py39', possible flavors: py38

I'm using poudriere to build my packages. My DEFAULT_VERSIONS looks like this:

DEFAULT_VERSIONS+= php=7.4 python=3.8 python3=3.8 pgsql=14 mysql=10.3m bdb=18

I have devel/py-jmespath@py38 and devel/py-jmespath@py39 both in my buildlist. devel/py-jmespath@py39 fails to build with the error from the subject.
Currently this is the only python port I have listed with py39 flavour, but I have built different php flavours before without problems.

The Makefile for py-jmespath lists:

USES=        python:3.7+
USE_PYTHON=    autoplist concurrent distutils

Is this expected because default python version is set to 3.8 or is it something that can be fixed?
I would advice to use only one version of python.
If i'm correct the current one is python3.9 and so in order to use it you don't need any line in make.conf.
I've had once a version conflict and solved it by manually removing the packages from,
[grep pythonXXX.YYY]
I only use one version of python on each host, but I have 80+ servers using pkg's built on the poudriere server.

I discovered I can configure BUILD_ALL_PYTHON_FLAVORS and then I can build different flavors of python ports.