Google N-gram Corpus Counts
╭─ーーーーー─┬────────┬───────╮
│ 行き届く　 │ 36,821 │ 95.0% │
│ 行届く　　 │    300 │  0.8% │ - adding (daijr/s, shinmeikai)
│ 行きとどく │    240 │  0.6% │ - sK
│ いきとどく │    430 │  1.1% │
│ ゆきとどく │    983 │  2.5% │
╰─ーーーーー─┴────────┴───────╯

@@ -8,0 +9,3 @@
+<keb>行届く</keb>
+</k_ele>
+<k_ele>
@@ -9,0 +13 @@
+<ke_inf>&sK;</ke_inf>

References:
- from a message i received
メールが行きとどかない場合はお知り合いの方にご連絡をお願いします。
- from the web - Google gives me the following number of exact matches: 行き届く 730, 行きとどく 749, 行き届かない 520, and 行きとどかない 409

To improve the function of "Text Glossing", i'd like to add the second spelling variant, since its usage seems common enough.

A note concerning Googits: when checking with Google in the context of making or modifying database entries here, i always use quotation marks around the query string. However, Google has the habit of showing, at the top, a hit number that is in many cases vastly larger than the number of hits that can actually be found - it looks like that large number includes whatever fuzzy matches Goolge deems appropriate. To get the number of exact matches i go forward in the list of displyed items until i reach (in most cases) the end of the list where a comment like this appears: 最も的確な結果を表示するために、上の749件と似たページは除外されています。検索結果をすべて表示するには、ここから再検索してください。

@@ -7,0 +7,3 @@
+</k_ele>
+<k_ele>
+<keb>行きとどく</keb>