IEV data anomaly (20201217): SOURCE modification not parsed out correctly

```
[FAILED TO PARSE SOURCE] in the synonym, "ambient" has been replaced by "active"
extract_source_clause 'in the synonym, "ambient" has been replaced by "active"'
[RAW] in the synonym, "ambient" has been replaced by "active"
{:source_ref=>"in the synonym, \"ambient\" has been replaced by \"active\"",
:clause=>nil,
:relation_type=>{:type=>:identical}}
[FAILED TO PARSE SOURCE] in the definition, "hypothetically possible" has been replaced by "typical" and "where AAL concepts, products and services may improve the quality of life" has been replaced by "in which active assisted living can be realized"
extract_source_clause 'in the definition, "hypothetically possible" has been replaced by "typical" and "where AAL concepts, products and services may improve the quality of life" has been replaced by "in which active assisted living can be realized"'
[RAW] in the definition, "hypothetically possible" has been replaced by "typical" and "where AAL concepts, products and services may improve the quality of life" has been replaced by "in which active assisted living can be realized"
{:source_ref=>
"in the definition, \"hypothetically possible\" has been replaced by \"typical\" and \"where AAL concepts, products and services may improve the quality of life\" has been replaced by \"in which active assisted living can be realized\"",
:clause=>nil,
:relation_type=>{:type=>:identical}}
[FAILED TO PARSE SOURCE] the note has been modified for clarity.
extract_source_clause 'the note has been modified for clarity.'
[RAW] the note has been modified for clarity.
{:source_ref=>"the note has been modified for clarity.",
:clause=>nil,
:relation_type=>{:type=>:modified, :modification=>"for clarity."}}

[FAILED TO PARSE SOURCE] dans le synonyme anglais, le mot "ambient" a été remplacé par "active"
extract_source_clause 'dans le synonyme anglais, le mot "ambient" a été remplacé par "active"'
[RAW] dans le synonyme anglais, le mot "ambient" a été remplacé par "active"
{:source_ref=>
"dans le synonyme anglais, le mot \"ambient\" a été remplacé par \"active\"",
:clause=>nil,
:relation_type=>{:type=>:identical}}
[FAILED TO PARSE SOURCE] dans la définition anglaise, "hypothetically possible" a été remplacé par "typical" et "where AAL concepts, products and services may improve the quality of life" a été remplacé par "in which active assisted living can be realized"
extract_source_clause 'dans la définition anglaise, "hypothetically possible" a été remplacé par "typical" et "where AAL concepts, products and services may improve the quality of life" a été remplacé par "in which active assisted living can be realized"'
[RAW] dans la définition anglaise, "hypothetically possible" a été remplacé par "typical" et "where AAL concepts, products and services may improve the quality of life" a été remplacé par "in which active assisted living can be realized"
{:source_ref=>
"dans la définition anglaise, \"hypothetically possible\" a été remplacé par \"typical\" et \"where AAL concepts, products and services may improve the quality of life\" a été remplacé par \"in which active assisted living can be realized\"",
:clause=>nil,
:relation_type=>{:type=>:identical}}
[FAILED TO PARSE SOURCE] la note a été modifiée à des fins de clarté.
extract_source_clause 'la note a été modifiée à des fins de clarté.'
[RAW] la note a été modifiée à des fins de clarté.
{:source_ref=>"la note a été modifiée à des fins de clarté.",
:clause=>nil,
:relation_type=>{:type=>:modified, :modification=>"à des fins de clarté."}}
```

Start by reproducing the listed English and French inputs to extract_source_clause, including the synonym, definition, and note examples. Inspect the source-parsing entry point named in the report and verify that these SOURCE modifications no longer produce FAILED TO PARSE SOURCE or a nil clause.

Written by the indexing model from the issue text.