You Say Collectable, I Say Collectible

Recently, I circulated a draft agreement that included a representation that a party's receivables were collectible.  The other side returned a draft that modified the representation and changed the spelling to "collectable".  Which is correct?

First, I checked to see how the word is spelt by the California courts.  Below are the results for published decisions in 2014:

Collectable

Collectible

Ducoing Management, Inc., 229 Cal.App.4th 1252 (2014) In Re Conservatorship of Estate of McQueen, 59 Cal.4th 602 (2014)
Southern Cal. Edison Co. v. P.U.C., 227 Cal.App.4th 172 (2014) Cardinale v. Miller, 222 Cal.App.4th 1020 (2014)
American Master Lease LLC v. Idanta Partners, Ltd, 227 Cal.App.4th 172 (2014) Rosen v. LegacyQuest, 225 Cal.App.4th 375 (2014
Scottsdale Indemnity Co. v. Nat’l Continental Ins. Co., 229 Cal.App.4th 1166 (2014)
Transport Ins. Co. v. Superior Court, 222 Cal.App.4th 1216 (2014)
Gray1 CPB, LLC v. SCC Acquisitions, Inc., 225 Cal.App.4th 410 (2014)

Next, I checked the redoubtable H.W. Fowler who asserts that the -ible form is the natural one for words derived from Latin verbs ending in ere or ire.  The only problem with this explanation is that it requires one to know whether an English word is derived from a third or fourth declension verb.  The word at issue is the adjectival form of the verb "collect".  It so happens that "collect" is derived from the Latin words cum (meaning together) and lego (meaning to read or choose).  Lego is a third conjugation verb (the present infinitive is legere).  Thus, according to Fowler, the "natural" form of the adjective is "collectible".