You have to be careful once you pass the 2 GB and 32 GB thresholds in SD cards. As shown here
https://www.sdcard.org/consumers/sdxc_capabilities/ , regular SD Cards have a maximum capacity of 2 GB and will work on any SD reader. Up to 32 GB uses SDHC and requires a SDHC or SDXC reader (that is, regular SD readers won't work). Once you get into 64GB territory, only SDXC readers work, not SDHC or SD readers.
Therefore, if a Kobo says that its maximum capacity is 32 GB, it *probably* means that it uses the SDHC standard. If a partitioned SDXC card works in a Kobo, then it means that it has an SDXC card reader and, possibly, a software restriction built into the OS.