Of course, if a researcher tampers with the evidence, making a unilateral, unsupported claim or assumption that a word means something that it does not, then that does not constitute semantic  it is what is known as dirty work at the crossroads, and M and S are indulging in a bit of mischief by suggesting that semantic change either has taken place or is taking place because they have some evidence that a certain change in usage had crept in.
( ( Of course ) ( , ( ( if ( ( a researcher ) ( ( ( tampers ( with ( the evidence ) ) ) , ) ( making ( ( a ( unilateral ( , ( unsupported ( ( claim or ) assumption ) ) ) ) ) ( that ( ( a word ) ( ( means something ) ( that ( it ( does not ) ) ) ) ) ) ) ) ) ) ) ( , ( ( ( ( ( then ( that ( ( does not ) ( constitute ( semantic ( it ( is ( what ( is ( ( known ( as ( dirty work ) ) ) ( at ( the crossroads ) ) ) ) ) ) ) ) ) ) ) ) , ) and ) ( ( ( M and ) S ) ( are ( ( indulging ( in ( ( a bit ) ( of mischief ) ) ) ) ( by ( suggesting ( that ( ( semantic change ) ( either ( ( ( has ( taken place ) ) or ) ( is ( ( taking place ) ( because ( they ( have ( ( some evidence ) ( that ( ( ( a ( certain change ) ) ( in usage ) ) ( had ( crept in ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) ) )
(ROOT (S (PP (IN Of) (NP (NN course))) (, ,) (SBAR (IN if) (S (NP (DT a) (NN researcher)) (VP (VBZ tampers) (PP (IN with) (NP (DT the) (NN evidence))) (, ,) (S (VP (VBG making) (NP (NP (DT a) (JJ unilateral) (, ,) (JJ unsupported) (NN claim) (CC or) (NN assumption)) (SBAR (IN that) (S (NP (DT a) (NN word)) (VP (VBZ means) (NP (NN something)) (SBAR (IN that) (S (NP (PRP it)) (VP (VBZ does) (RB not))))))))))))) (, ,) (S (ADVP (RB then)) (NP (DT that)) (VP (VBZ does) (RB not) (VP (VB constitute) (ADJP (JJ semantic) (SBAR (S (NP (PRP it)) (VP (VBZ is) (SBAR (WHNP (WP what)) (S (VP (VBZ is) (VP (VBN known) (PP (IN as) (NP (JJ dirty) (NN work))) (PP (IN at) (NP (DT the) (NNS crossroads)))))))))))))) (, ,) (CC and) (S (NP (NNP M) (CC and) (NNP S)) (VP (VBP are) (VP (VBG indulging) (PP (IN in) (NP (NP (DT a) (NN bit)) (PP (IN of) (NP (NN mischief))))) (PP (IN by) (S (VP (VBG suggesting) (SBAR (IN that) (S (NP (JJ semantic) (NN change)) (VP (CC either) (VP (VBZ has) (VP (VBN taken) (NP (NN place)))) (CC or) (VP (VBZ is) (VP (VBG taking) (NP (NN place)) (SBAR (IN because) (S (NP (PRP they)) (VP (VBP have) (NP (NP (DT some) (NN evidence)) (SBAR (IN that) (S (NP (NP (DT a) (JJ certain) (NN change)) (PP (IN in) (NP (NN usage)))) (VP (VBD had) (VP (VBN crept) (PP (IN in))))))))))))))))))))) (. .)))
When researchers apply the label semantic, they always do so with great care.
( ( When ( researchers ( apply ( ( the label ) semantic ) ) ) ) ( , ( they ( always ( ( ( do so ) ( with ( great care ) ) ) . ) ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NNS researchers)) (VP (VBP apply) (S (NP (DT the) (NN label)) (ADJP (JJ semantic)))))) (, ,) (NP (PRP they)) (ADVP (RB always)) (VP (VBP do) (ADVP (RB so)) (PP (IN with) (NP (JJ great) (NN care)))) (. .)))