One gets the impression that the editors of L used the good stuff from the W and substituted their own, much better material when they encountered some of the bad stuff.
( One ( ( ( gets ( the impression ) ) ( that ( ( ( the editors ) ( of L ) ) ( ( ( ( used ( the ( good stuff ) ) ) ( from ( the W ) ) ) and ) ( substituted ( ( their ( own ( , ( ( much better ) material ) ) ) ) ( when ( they ( encountered ( some ( of ( the ( bad stuff ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP One)) (VP (VBZ gets) (NP (DT the) (NN impression)) (SBAR (IN that) (S (NP (NP (DT the) (NNS editors)) (PP (IN of) (NP (NNP L)))) (VP (VP (VBD used) (NP (DT the) (JJ good) (NN stuff)) (PP (IN from) (NP (DT the) (NNP W)))) (CC and) (VP (VBN substituted) (NP (NP (PRP$ their) (JJ own) (, ,) (ADJP (RB much) (JJR better)) (NN material)) (SBAR (WHADVP (WRB when)) (S (NP (PRP they)) (VP (VBD encountered) (NP (NP (DT some)) (PP (IN of) (NP (DT the) (JJ bad) (NN stuff))))))))))))) (. .)))
The editors appeared to have subsitited nothing when working on W. 
( ( The editors ) ( appeared ( to ( have ( ( subsitited nothing ) ( when ( working ( on W. ) ) ) ) ) ) ) )
(ROOT (S (NP (DT The) (NNS editors)) (VP (VBD appeared) (S (VP (TO to) (VP (VB have) (VP (VBN subsitited) (NP (NN nothing)) (SBAR (WHADVP (WRB when)) (S (VP (VBG working) (PP (IN on) (NP (NNP W.)))))))))))))