The SDAs have extensive evangelism in Africa, South America and China and his is what builds their numbers. I also don't think the 35 million is accurate.
The SDAs are facing problems at this time there could be two Adventist churches soon because differences between them are being promoted. The general conference is at odds with the unions and conferences over compliance in five areas. Womens ordination, Church doctrine, Homosexuality, Evolution etc. Five committees have been set up to ensure compliance and the unions and conferences are upset. Disciplinary action has been talked about by the General conference such as shaming conference leaders before they are allowed to talk in committees. Many conferences have written to the General conference objecting to such unchristian and undemocratic suggestions. Many women have been made pastors by the conferences and is a thorn in the side of the general conference. Also the SDAs are not a creedal church but the General are trying to make the 28 fundamentals a creed. Time will tell what will happen