Paul
I'd encourage you to use the Mosaic Dataset - it's dramatically improved over the raster catalog.
Create a separate "source" mosaic dataset for each year, and when you add rasters, have Update Cell Size Ranges on (default) to calculate visibility based on pixel size. Add a field into the Attribute Table for "year". You'll have to populate that field manually. If your different years are in different projections, create each source mosaic dataset in the original data projection.
Then create a new mosaic in the projection for the base map (web mercator aux. sphere?) and input the single-year mosaics, being sure to use RasterType = TABLE, and also be sure Update Cell Size Ranges is OFF (so the visibility vs. resolution is maintained from the original source mosaics). We refer to this as a "derived" mosaic dataset, but note you create it just like any other. (It's not fundamentally different like a Referenced mosaic dataset; you should learn about those, too, if you haven't used them)
I see you're on 10.2, so from the derived Mosaic Dataset, you can create image caches using ArcGIS Desktop and those cache datasets will be your base maps.
When viewing or creating a base map cache, set the Mosaic Method to "By Attribute", and select "LowPS" --> this will display the highest resolution image in any area. Alternatively, with Mosaic Method to "By Attribute", and field "year" (DESELECT "order ascending" since when mosaicking by attribute, smaller numbers have higher priority - otherwise the OLDEST images will appear on top).
This should work, *unless* you're going to cache your base maps at 0.5 feet, in which case the software will automatically put the highest resolution images on top (even if not the most recent) when you zoom to full resolution in the "newest on top" version. Let me know if you need more guidance on this issue.
Note Mosaic Method is a property of the Mosaic Dataset; you can set the default by right clicking the MD in Catalog, or after loaded into the map, change it by right clicking the Image layer of the MD in the table of contents (see "Mosaic" tab).
I think I've covered everything, but test it and if something doesn't work, let me know.