There would have been geographic (and perhaps ethnic background .... And wealth status ... And perhaps even religious affiliations) that made more likely who migrated, who didn't.
I've read my Scotch Irish from Augusta VA & the corner where NC & TN meet had even within the family divisions of Tory vs Whig (Loyalist vs Patriot).
I wonder though if more recent immigrants from Europe, such as the Palatines, had the same British Crown allegiance ?
In a short synopsis the Palatinate was a country within present day Baden-Württemberg in Germany along the east side of the Rhine River. As part of the Holy Roman Empire life may have been tough, but when the Empire was broken down in the 15th or 16th century, it got worse. The little ice age was in full swing so between severe weather causing poor crop production; no help from a Papist government due to religious conflict (Palatines were principally Protestant, Lutheran specifically); and wars being waged through the area, the people known by some as "The Poor Palatines," were starving and bedraggled.
A little after 1600 (there are more specific years), a massive migration out of the Palatinate, and surrounding countries with similar stories began. Over the next few decades tens of thousands moved northward to English held lands in hopes of better lives, and Britain made those hopes reality. Extreme loyalty to a country that in a big way saved your progeny from starvation is not hard to imagine, hence many were Loyalists.
Some stayed in the Netherlands, Belgium, Normandy and the British Isles, and some of these migrated later to America. The later groups often came straight to North America to colonies on both sides of today's border. None of them forgot England's generosity. My own family is among the latter, though other branches of the name may have been earlier.
Erica Howton the key to membership in the Palatines is simple really. The massive migrations took place in the era noted in this project, from the Palatinate. Other regions share the name "Palatinate" and most still qualify for this dubious distinction. Emigration dates, and places on the fringes of this territory are Palatines in my eyes if they share a similar story. The story is really told today by the migration patterns.
Once reaching the Colonies, the pattern is not so clear. In my own family, one brother went to North Carolina and pretty much stayed even 'til today; the other went to New Jersey and moved westward. The sister stayed in Pennsylvania, where she arrived.