The cause of these complaints was found to be the timing differences between the issuing of the two documents by the two services and the failure of some items electronic and posted to arrive at all.
Nodwyd mai achos y cwynion hyn oedd y gwahaniaeth amser rhwng anfon y ddwy ddogfen gan y ddau wasanaeth a methiant rhai eitemau electronig a phost i gyrraedd o gwbl.