JW publications strongly imply that the "Heavenly Calling" ended in 1935, but aren't quite definite. Here's a small sampling. Notice the use of terms like "evidently," "suggested," "reasonable to conclude," "about complete," "virtually complete," etc.
*** re chap. 19 p. 116 Sealing the Israel of God ***
The general selection of the true Israel of God proceeded from the day of Pentecost 33 C.E. down to 1935 when, at a historic convention of Jehovah’s Witnesses in Washington, D.C., emphasis was shifted to the ingathering of a great crowd with earthly life prospects (Revelation 7:9)
*** re chap. 20 p. 125 A Multitudinous Great Crowd ***
They were no part of the little flock but rather of the other sheep. (Luke 12:32; John 10:16) Their being identified in 1935 as the great crowd of other sheep was an indication that the choosing of the 144,000 was then about complete.
*** w88 1/1 p. 11 The Last Days—A Time of Harvest ***
8 However, they are not alone. John, in another vision, sees the sealing of the final ones of the 144,000. (Revelation 7:1-8) Evidently, the gathering of these was virtually complete by 1935. But then, John reports, he sees "a great crowd, which no man was able to number, out of all nations and tribes and peoples and tongues, standing before the throne and before the Lamb." (Revelation 7:9-17) So the harvest work continues as many more from "the peoples, national groups and languages" start to serve Jesus as King.
*** ws chap. 6 p. 49 On the Watch During "the Conclusion of the System of Things" ***
6 In the mid-1930’s, something significant took place. What occurred suggested that the membership of the spiritual bride of Christ had been filled, that there were on earth enough spirit-begotten disciples of the Bridegroom to make up the full number of his heavenly bride.
*** w82 2/1 p. 28 "Born Again"—Man’s Part and God’s Part ***
16 Those sharing in preaching this good news of the Kingdom in modern times are confident that Jehovah God is leading his dedicated servants by means of his visible spirit-begotten organization, the "faithful and discreet slave." (Matthew 24:45-47) Under its direction the heavenly hope was held out, highlighted and stressed until about the year 1935. Then as ‘light flashed up’ to reveal clearly the identity of the "great crowd" of Revelation 7:9, the emphasis began to be placed on the earthly hope. (Psalm 97:11) It is reasonable to conclude, therefore, that by that time the full number of 144,000 would have been nearly completed. Of course, any individuals proving unfaithful would need to be replaced. But, understandably, these would be comparatively few
*** w82 2/15 p. 30 "What Prevents Me from Getting Baptized?" ***
15 When we consider how Jehovah has been dealing with his people during the ‘harvest period,’ it seems evident that the heavenly calling in general was completed about the year 1935, when the hope of the "great crowd" of Revelation 7:9-17 was properly understood to be an earthly one.