Are you importing the sketchup file into layout and subsequently pulling up those scenes or are you importing 2d images exported from those sketchup scenes.
If you have imported the sketchup file into layout and pulled up various scenes, if you create new scenes in that same SU file and save it. When you open the exisitng layout document and update the SU reference file, those new scenes will be available to show/open.
Don’t use the “send to layout” command. Save the sketchup file, then open your exisitng Layout file and update that SU reference, then the new scens will be available to show in that Layout document.
I could be wrong as I’ve never used the send to layout command, but it may be for the original creation only, but once the layout doc is created and it has the SU file in it to reference, you only ever then need to change the SU file and update it in LO.