Question about acquire and release images from and to external queue

https://github.com/KhronosGroup/Vulkan-Docs/blob/cee0f4b12acde766e64d0d038b03458c74bb67f1/chapters/synchronization.txt#L4600

In the spec, it says

If the transfer is via an image memory barrier, and an image layout transition is
desired, then the values of oldLayout and newLayout in the
_release operation_'s memory barrier must: be equal to values of
oldLayout and newLayout in the _acquire operation_'s memory
barrier.

However, if the src queue is external, we may not know the oldLayout.
For example, For GL EXT_external_objects extension, there is no API to query the current image layout
before calling SignalSemaphoreEXT(). In that case, what should we use for the oldLayout.