Whilst the National Records of Scotland is now an amalgamation of what was once the GRO and the Scottish Record Office/National Archives of Scotland, back in the 1990s they were completely separate. Apart from a few anomalies the Kirk Sessions were always held by the Scottish Record Office/National Archives of Scotland. To this day, even though both come under the new new name (the National Records of Scotland), and there is some overlapping with staff, they are still very separate organizations. I cannot imagine the GRO staff would have done a Kirk Session search for you. The Scottish Record office/National Archives of Scotland may have done but they would not have had the authority to write out an official OPR extract, which is what you have. This is a legally binding document, the same principles apply as if a living person was to order a copy of a birth certificate today. Whilst mistakes could have been made, e.g. perhaps the spelling is wrong, it will have been made from an OPR.
As for the Kirk Sessions, well I keep hearing that they will go online soon but… we’re still waiting. I know the SP site is to have a major overhaul in 2016 so I wonder if they are waiting for that. The reality is that it would be very hard to index Kirk Sessions and so many feel they could only be published on a subscription site; this is of course a major deviation from the SP model at the moment.
I am Emma Maxwell of Scottish Indexes by the way, just in case you hadn’t made the connection.
Emma