To say that "Jehovah is the Lamb" is a little misleading . When ever we used to read Rev 21.4 we always understood it to refer to God "Jehovah" , not Jesus "The Lamb". When we studied the Rev Book (how many times?) nobody queried why the Lamb was used in the paragraph. I think that they saw the anomaly and changed it .As a get out they could point to the Rev book page 9 , old book
"It is not claimed that the explanations in this publication are infallible .At the same time time, however, we firmly believe that the explanation set forth herein harmonize with the Bible in its entirety......."