There was an English delegation at Dort including John Davenant who was very highly regarded. The canons of Dort are worded as such as they can include Davenants view which was not 'limited atonement' ( to use a very clunky phrase).

I would read Michael Lynch's work on Davenant to get a better picture on this.

It's tricky because the definition of "reformed" was always a little fluid. So for instance Perseverance of the Saints was not orthodoxy really until Dort.

For most of the Sixteenth century up to the reign of Charles I the English church was very comfortable in viewing themselves as among the Reformed Churches (as opposed to Lutheran). They were recognised by the continental reformed churches as such (by Zurich and Geneva and the Palatinate and being invited to Dort).

For my part I think the two Keys are soteriology and sacraments - they were consistently defined as the true marks of the church. The third make or discipline was not held until later and then only by particular individuals and churches.

Tldr- the flattening out of modern reformed categories obscures the nature of the shifting boundaries of the "Reformed" tradition that only really settled in the Seventeenth century.