@Shibui ...thanks for replying
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For some unknown reason I googled about repotting the Ginko - normally I just go ahead and trim as for my other trees in bonsai pots. Could have been because of checking to see if anything about reducing for going to a less deeper pot - the only reason I can think! The new pot not having the depth as the present one. If container grown trees then I gradually reduce.
The other source was Bonsai Empire - brief mention not to prune heavily, in their guide for Ginko. I've had Ginko previously when I first started Bonsai, 25'ish years ago, but lost to frost - no Internet etc., back then for the now easily available information. My books didn't mention about susceptibility for frosts when in pots.
My present one I've had for about 4 years - online raffle - arrived in a broken pot. Repotted into a deeper one (about 3½") because it was all I had at the time. Last year repotted into another (2½") and noticed roots coming from drainage holes. I hadn't intended to repot again this year - supposed to be every 3~5 years apparently - but surprised to find the roots in the drainage holes. I cut the holding wires to try and pull out from the pot to check density but couldn't move it - holding in very tight. I'm going to have to cut round the inside of the pot to release.
Thanks again for sharing your experiences with Ginko and the handling of the roots when repotting - very much appreciated.