The battles were in April and June of 1775; “the ensuing spring” would mean that the year is 1774.
Winter came on; it rapidly passed away. Spring advanced ...
1774 changes to 1775.
The spring opened ... the colonies, which had now been dissevered from the British empire, by the declaration of independence
This is the same spring as in the previous quotation, but if the Declaration of Independence (July 1776) is in the past, it would have to be the spring of 1777.
It was at the latter end of the month of May ...
May 1775 or 1777, depending on one’s chosen chronology.
The particulars of this action, in the early stage of the American war, are yet remembered by many.
The “action” may be a conflation of two different episodes involving the Trumbull, neither of them early in the war: the first was in June 1780, the second in late August 1781. The Trumbull was towed to New York, not to London.
... who died there about eighteen months ago ...